I agree that RF sense is sort of risky with fast CW. It's not even ideal for
SSB but is tolerable. Lots of accessories, even some power amplifiers have used
it (for example, most 2 meter amplifiers).
If you are using Ten Tec transceivers, recent ones anyway, you would not be hot
when using the PTT line for switching because you would use the closed loop
keying that Ten Tec has already implemented in their radios. You would never
hot switch because no RF could flow until the switching relay was closed. If
you are using a QSK linear, you would route the "relay closed" feedback from
the linear to control the RF permission for the XCVR. The linear would be keyed
by an output from the preselector so that, at no time would there be RF on the
preselector until all relays were in proper position.
The relays in the preselector need not be heavy clunky things so they should
change quickly. They could even be PIN diodes at 100 watt power levels.
As you may know, I am not a be fan of drilling holes in chassis of commercially
made equipment. Not only are warranties voided, but she repair facilities will
not even service modified radios.
Also, being a radio reseller, I cringe when I have to explain away such added
holes and jacks to a potential buyer.
Gary
Sent from my iPad
> On Sep 13, 2016, at 8:33 AM, rick@dj0ip.de <Rick@DJ0IP.de> wrote:
>
> But that was yesterday.
> What do people do today?
>
> I'm not a fan of RF sensing. Hot switching? No thanks.
> You may get away with it in SSB but not in CW.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt, Germany)
>
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Gary J
> FollettDukes HiFi
> Sent: Tuesday, September 13, 2016 3:07 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Scads of used Icom IC-7300
>
> Several preselectors were produced by commercial vendors, some time ago, not
> likely as good a preselector as yours, but they offered RF sensing to pass
> the TX signal around the preselector.
>
> This seems to be a better solution than modifying the radio.
>
> For those not comfortable with RF sense switching, one might consider using
> the PTT line to switch around the preselector.
>
> With most TT radios, these lines are very fast (for QSK) and could be in
> parallel with the linear key line if a linear is used.
>
> ‘Gary
>
>
>
>> On Sep 13, 2016, at 5:55 AM, rick@dj0ip.de <Rick@DJ0IP.de> wrote:
>>
>> Correct, my pre-selector is RX only, which the name implies.
>> That is why every transceiver I have had since the mid 70's was
>> immediately modified with two RCA phono jacks mounted on the back. I
>> interrupt the RX ANT line internally and run it thru the two jacks,
>> jumpered of course when no preselector is attached. Even my Eagle has
>> this mod. The OM7 had it available but very few people performed the
>> mod. I did it on the OM7 I tested here prior to its announcement and
>> it made a WORLD of difference on 40m.
>>
>> 73 - Rick, DJ0IP
>> (Nr. Frankfurt, Germany)
>>
>>
>>
>> -----Original Message-----
>> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of
>> shristov
>> Sent: Tuesday, September 13, 2016 10:15 AM
>> To: Discussion of Ten-Tec Equipment
>> Subject: Re: [TenTec] Scads of used Icom IC-7300
>>
>> "rick@dj0ip.de" <Rick@DJ0IP.de> wrote:
>>
>>> However the Dunestar SPECS on their web site claim 40dB band-to-band
>>> rejection. I was just quoting the specs.
>>> http://www.dunestar.com/store/Single-Band-Bandpass-Filters-pid-4.html
>>
>>
>> Hi Rick,
>>
>>
>> that's what I had in mind.
>> Taking the 7 MHz filter as an example, there is 40 dB attenuation on
>> ~3.5 MHz.
>>
>> But on 6 MHz the attenuation is practically nil.
>>
>> Your preselector is the right tool for the job.
>> But it's receive-only, given the 7.5 dB passband attenuation.
>>
>> Dunestar etc filters must have a much wider passband in order to
>> achieve low enough passband attenuation, making them suitable for
>> transmitting.
>>
>>
>> Best 73,
>>
>> Sinisa YT1NT, VE3EA
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